1. Field of the Invention
The present invention relates to a detector device using magneto-resistors for detecting the movement of a moving body and more particularly for detecting a rotation of a rotating body and a straight movement of a moving body.
2. Description of the Prior Art
There are conventional known varieties of movement detector devices for monitoring moving bodies,each device serving to detect rotational movement of rotators and straight advance movements of moving bodies.
FIG. 1 illustrates an exemplary detection of the rotation of a motor shaft 2 with use of a movement detector device (rotation sensor)1. In the same figure, the motor shaft 2 includes a gear 3 to be detected fitted thereover. To a peripheral surface of gear 3, a detection surface of the movement detector device 1 is opposed via a gap. The gear 3 is made of a ferromagnetic material
As seen from FIG. 2, the movement detector device 1 includes a casing 4 and a magnet 5 that generates a bias magnetic field. On the upper end surface of magnet 5 are disposed four magneto-resistors MR.sub.A 1, MR.sub.A 2, MR.sub.B 1 and MR.sub.B 2 as illustrated in a circuit diagram of FIG. 3, the magneto-resistors MR.sub.A 1 and MR.sub.A 2 being connected in series with each other to construct a first phase detector circuit. The magneto-resistors MR.sub.B 1 and MR.sub.B 2 are also connected in series with each other to construct a second phase detector circuit.
The first phase detector circuit and the second phase detector circuit are interconnected in parallel with each other. One end of the parallel circuit is connected to a power source line 6 and the other end is connected to a ground line 7.
A first phase detection signal is taken out from a connection portion between the magneto-resistors MR.sub.A 1 and MR .sub.A 2 while a second phase detection signal is taken out from a connection portion between the magneto-resistors elements MR.sub.B 1 and MR.sub.B 2.
These magneto-resistors MR.sub.A 1, MR.sub.A 2, MR.sub.B 1, and MR.sub.B 2 are disposed, with respect to the gear 3 to be detected, as illustrated in FIG. 4. More specifically, when the magneto-resistors MR.sub.A 1 and MR.sub.B 1 are opposed to the crest 3a of one tooth of the gear 3, the magneto-resistors MR.sub.A 2 and MR.sub.B 2 are opposed to the root 3b between two teeth of the gear 3. Therefore, with a pitch of the teeth of the gear 3 assumed to be T, MR.sub.B 1 is shifted in phase by T/4, MR.sub.A 2 by T/2, and Mr.sub.B 2 by 3T/4 with respect to the magneto-resistor Mr.sub.A 1.
Herein, designated at 8 (FIGS. 2 and 3) are terminals for the power supply line 6, for the ground line 7, and for taking out the detection signals from the, magneto-resistors. Terminals 8 are connected to detector circuits of the respective magneto-resistors via a lead frame 10.
The movement detector device 1 is opposed to the gear 3. With the motor shaft 2 rotated a first phase detector circuit signal and a second phase detector circuit signal are picked up during time periods separated by T/4, with respect to each other as illustrated in FIG. 5. Analyses of the signal voltages clarify the amount of the rotational movement, rotational speed, and revolutions of the motor shaft 2. Further, the pick-up of the signals of two different phases allows an estimation of the direction of rotation of the motor shaft 2.
In order to raise the resolution of such rotation detection using the above movement detector device 1, however, a use should be made of a gear of a small module where a pitch T of the teeth of the gear 3 is replaced by a smaller pitch. Further, since a gap G existing between the detection surface of the movement detector device 1 and the gear 3 is increased, the sensitivity of the device is decreased. Therefore, it is necessary to decrease the gap G.
However, provided that the module of the gear 3 is decreased to reduce a pitch interval of the gear, the number of magneto-resistors disposed within that pitch can not be increased. Additionally, as the pitch of the teeth is decreased, a detection output is reduced as illustrated in FIG. 6. Hence, if the detection output is to be increased correspondingly, and, if it is to be detected the gap G between the gear 3 and the detection surface of the movement detector device 1 must be further reduced.
With the gap G made very small, however, it is difficult to position the movement detector device 1, and since the gear 3 is almost certain to be at least a little eccentric, there is a problem of the teeth of the gear 3 possibly making contact with the detection surface of the movement detector device 1. To avoid the just-mentioned problem, there is a difficulty of accurately machining gears and the device assembly so that the gear 3 must be machined without causing any eccentricity and with an almost religious care.
Further,in the prior art movement detector device, the detector circuits of the magneto-resistors in the respective phases are connected in parallel to each other and between the power supply line 6 and the ground line 7, so that an application of voltage to each detector circuit of each magneto-resistor in each phase becomes greater. Accordingly, as the detector circuits of the magneto-resistors are constructed in multiple phases, the power consumption is severely increased and the heat produced by the increase of the power badly affects the detection performance.